Device for automatically controlling electrical conditions of an electron beam unit

ABSTRACT

A power supply of an electron beam unit has switching components and comprises means which enables the power supply to operate both as a current source and as a voltage source, said means being in the form of at least one reactive component connected in the circuit of the power supply by at least one of its switching components.

United States Patent 1191 Brukovsky et a1.

DEVICE FOR AUTOMATICALLY CONTROLLING ELECTRICAL CONDITIONS OF AN ELECTRON BEAM UNIT' Inventors:- Igor Pavlovich Brukovsky, 1,

Filed:

Mosfilmovskypereulok, 5, korpus 2-B, k v. 16; Pavel Borisovich' Yakovlev, ulitsa Tolbukhina, 9, korpus 1, kv. 15; Kirill Davidovich Gutterman, 3 Tversk'aya-Yamskaya ulitsa, 29, kv. 8; Alexandr Vasilievich P'erov, Pervomaiskaya ulitsa, 69, kv. 28, all of Moscow; Vladimir Fedorovich Zhukov, ulitsa Cheljuskintsev 3, kv. 21, Rzhev Kalininskoi Oblasti; Larisa Petrovna Nekrasova, Sovetskaya ploschad, 10, k'v} 36, Rzhev Kalininskoi Oblasti; Jury Dmitrievich I'vanovsky, ulitsa Mayak-ovskogo, 4, kv. vl5, Rzhev Kalininskoi Oblasti, all of USSR.

Se t-1 1971 ApplaNoJ 181,466

Related US. Application Data Continuation-impart of Ser. No. 841,815, July 15, 1969, abandoned.

[ Sept. 1-1, 1973 US. Cl 315/137, 315/200, 315/291,

Primary ExaminerRoy Lake Assistant Examiner-Lawrence J. Dahl Attorney.lohn C. Holman et a1.

[57] ABSTRACT A power supply of an electron beam unit has'switching components and comprises means which enables the power supply to operate both as a current source and as a voltage source, said means being in the form of at least one reactive component connected in the circuit of the power supply by at least one of its switchlng'components.

3 Claims, 12 Drawing Figures Power: suPPLY- ELECTRON HEATlNG 7 DEVICE l4 PATENTEDSEPI 1 Im 3.758.816

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- sum 2 or 3 r ELECTRON uamfme DEVlCE e F/G] m! 5 DEVICE FOR AUTOMATICALLY CONTROLLING This application is a continuation-in-part of Applicants copending application, Ser. No. 841,815 filed July 15, 1969 now abandoned.

BACKGROUND OF THE INVENTION The present invention relates to electrothermics and, more particularly, to power supplies for electron beam units,

. Devices exist for supplying electron beam units, which devices are designed as voltage sources. How ever, a disadvantage of such devices is that they cannot be utilized as current sources.

Also in existence are devices for supplying electron beam units, which devices are designed as current sources. A disadvantage of these devices is that they cannot be utilized as a voltage source.

- An object. of the instant invention is to provide a power supply for an electron beam unit, which power supply would be suitable for .use both as a voltage source and as a current source. With this object in view, a power supply for an electron beam unit constructed' in accordance with the instant invention has switching components and preferably comprises means BRIEF DESCRIPTION OF THE DRAWING The invention itself will be better understood from the following detailed description of a preferred inventive embodiment, such description making reference to the accompanying drawings, in which:

FIG. 1 is a diagrammatic representation illustrating a load being supplied from a voltage source;

FIG. 2 is an illustrative diagram depicting a load being supplied from a current source;

FIG. 3 is a graphical illustration of the parameter characteristics of both a voltage source and a current source;

FIG. 4 depicts the current-voltage characteristics of a typical electron gun and different cathode temperatures;

FIG. Sis a schematic diagram depicting a singlephase modification of a power supply for an electron beam unit constructed in accordance with the instant 'invention;

FIG. 6 is a schematic diagram depicting a three-phase modification of the power supply in accordance with the instant invention;

FIG. 7' is a schematic illustration of the novel device of FIG. functioning as a voltagesource;

FIG. 8 depicts the three-phase modification of the device as shown in FIG. 5 functioning as a current source; I

FIG. 9 depicts the three-phase modification of the power supply of FlG. 6 functioning as a voltage source;

FIGS. 10 through I2 depict further switching con- 1 nections of the novel circuit of FIG. 6 functioning as a voltage source.

DESCRIPTION OF PREFERRED INVENTIVE EMBODIMENT As additional background so as to enable a clear understanding of the novel concepts of the instant invention, it should be understood-that there exists two entirely different varieties of supply sources for an electrical apparatus, these different types being voltage sources and current sources. These two sources can perhaps be best understood by the following.

An example of a load R being supplied from what is termed a voltage source is illustrated by the diagram shown in FIG. 1. The characteristic of the voltage source itself is shown in FIG. 3 (line 1). It should be understood from the characteristic that in this case the value of the supply source voltage within the operating range practically does not depend on the resistance value of the load R.

An example of a load R being supplied from what is termed a current source is illustrated by the diagram shown insFIG. 2 for the case when the reactance values ofan inductance and capacitance are equal in modules lX l [X The characteristic of the current source is shown in FIG. 3 (line 2). It should be clear from the characteristic that in this case the current value of the supply source within the operational 'range practically does not depend on the resistance value of the load R. Continuing with this background, it is known that the operation of industrial apparatus having electron guns, with non-uniform gas formation in the working chamber, involves a considerable number of electrical breakdowns between the anode and the cathode of the electron gun. An electrical breakdown between the electron gun electrodes is s short-circuit with respect to the apparatus supply source. The largest number of breakdowns occurs at the initial degassing stage of the material being remelted and in the course of melting.

At the end of the melting process practically no break-- downs occur since the metal has been sufficiently degassed.

In cases when the apparatus is supplied from a voltage source an electrical breakdown between the electrodes results in a considerable increase of current flowing through the supply source and the load (electron gun). This is an emergency mode, and to overcome it the supply source must immediately be disconnected from the supply mains. If breakdowns occur frequently enough, the supply source and the electron gun operate under the effect of heavy short-circuit currents which tend to reduce service life and impair the reliability of operation.

When the apparatus is supplied from a current source, an electrical breakdown between the electron gun electrodes (load short-circuiting) results in a drop of voltage across the electrodes to a value dependent on the conditions in which a discharge may spark over between the electron gun electrodes due to the electrical breakdown. As a rule, the discharge is unsteady in character, breaking spontaneously after a time interval (0.0l-0. 5 sec..), whereupon the voltage across the electron gun returns to the level preceding the electrical b'reakdown between the electrodes.

Consequently, when the apparatus is supplied from a current source, current of a given value always flows through the supply source and the electron gun, thus enhancing the reliability of operation and making it possible to use electrical equipment having a smaller overload capacity for supplying the apparatus than in the case of a voltage source used as supply.

The employment of a current source for supplying electron gun apparatus, however, raises certain difficulties due to the need to adjust the apparatus power, generally to control thetemperature of the cathode emitting electrons.

I FIG. 4 shows the characteristic of the electron gun at different cathode temperatures T, T T The area-A in the drawing is the area where the current is limited by the spatial discharge for a cathode at temperature T to which the Lengmur law I pU" applies. The area B is the saturation area, in which the current of the electron gun is described by the Richardson equation I SAT [exp b/T], where S is the cathode surface, A and b are Richardsons constants and T is the cathode temperature.

Obvio usly when the electron-gun apparatus is supplied from a voltage source, the apparatus power can gradually be reduced from the rated value to zero by varying thecathode temperature.

When the electron-gun apparatus is supplied from a current source the possibilities of power variations are limited. It is clear from FIG. 4 that if the apparatus operates at point a (intersection point of the supply source characteristic I const, and the electron-gun characteristic corresponding to the cathode temperature T the raising of the cathode temperature from T to T, will enable one to decrease the apparatus power not to zero but to a value depending on the coordinates of the point b.

A further increase in the cathode temperature will not cause the power to drop, since in the operation left of the point b the current of the electron gun is limited by a spatial discharge. The impossibility of gradually controlling the power from the rated value down to zero is a drawback of current sources when used for supplying electron guns, because the power must be gradually reduced at the end of the melting to prevent the formation of a shrinkage pipe in the ingot cast.

When the present apparatus is used for supplying electron gun installations, at the initial stage and in the course of melting the supply source functions as a current source, i.e., it has the characteristic 2 in FIG. 3, displaying all the advantages of current sources.

At the end of the melting process, when the power has to be gradually reduced, the supply source functions as a voltage source, i.e., it has the characteristic 1 in FIG. 2.

The change of the'supply source from one operating mode to the other is effected by connection or disconnection of reactive elements (capacitances or inductances) from the supply transformer with the help of contacts, controllable valves functioning as keys, or other switching elements, which connection or disconnection can be automatically effected at the desired times by non-illustrated conventional control means for operating the contacts and the like.

The reactive and switching elements which make is possible to change the operating mode of the supply source have been termed a means which enables the power supply to operate both as a current source and as a voltage source."

It will further be noted that the circuits allowing the supply source to operate with the characteristic 2 in FIG. 3 and the switching elements may be of various types.

With this background now, attention is directed to FIG. 5 showing a schematic diagram of the device (single-phase variant) for supplying an electron beam apparatus.

The device 4 for supplying the electron beam heating apparatus preferably comprises a matching transformer 5 connected at one end to the phase 1 of a three-phase supply mains, the other end of the transformer winding being connected to an inductance 6 which is connected to the phase 2 of the supply mains whose voltage leads the voltage in the phase 1 by The phase 3 of the supply mains, in which the voltage leads the voltage in the phase 2 by 120, is connected to a capacitance 8 through a cut-off switching element 7, the other end of the capacitance being connected to the inductance 6 and to the matching transformer 5.

A closing switching element 9 is connected across the two ends of the inductance 6. The secondary winding of the matching transformer S is connected to a rectifier 10, whose negative terminal is connected to the cathode 11 of the electron gun of an electron beam heating apparatus 12, while the positive terminal is connected to metal 13 to be heated, which is at ground potential, similarly to the anode 14 of the electron gun.

FIG. 6 shows a schematic diagram of the device (three-phase variant) for supplying the electron beam heating apparatus.

The circuitry shown in this Figure is a combination of three single-phase circuits shown in FIG. 5 which are so connected that each of the primary windings of the three-phase matching transformer 15 is connected to the respective phases 1.2 and 3 of the supply mains through cut-off switching elements 16. The other ends of the transformer windings are connected to capacitances 17 connected to the respective phases of the supply mains through cut-off switching elements 18. One of the ends of each of the inductances 19 is connected to the winding of the transformer 15 and to the capacitance 17, while the other end is connected to the phase of the supply mains in which the voltage leads by 120 the voltage in the phase connected to the winding of the transformer 15. A closing switching element 20 is connected across the terminals of the inductance 19.

The ends of the windings of the transformer 15, connected to the switching elements 16, are connected to closing switching elements 21, whose other ends are interconnected with one another.

The end of the winding of each phase of the transformer 15, connected to the switching element 16, is connected through a closing switching element 22, to the beginning of the transformer winding connected to the phase in which the voltage leads the voltage in the initial phase by 120.

The secondary winding of the matching transformer 15 is connected to a three-phase rectifier 23, whose negative terminal is connected to the cathode of the electron gun of the electron beam heating apparatus 24, while the positive terminal, connected to the metal being heated, is held at the ground potential.

It is understood from the drawing that the means enabling the supply source to function as a current source With the above means functioning as a voltage source, two types of operation may take place. In the first type, the switching'element 7 is open and the.

switching element 9 is closed the circuit having the diagram shown in FIG. 1.

In the second type of operation, with the device functioning as a voltage source, the switching elements 7 and 9 are open and the circuit thus formed is illustrated in FIG. 7. This connection of the supply source is used in cases when there is a threat of an electrical breakdown in the electron gun. In this case, the inductance 6 connected in series with the winding of the transformer 5 limits the short-circuit current.

In a three-phase version'of the device functioning as a current source, the switching elements 16 and 18 are closed and the switching elements 20, 21 and 22 are open. FIG. 8 illustrates such a circuit.

For a voltage-source operation, four variants are possible in the circuit operation: f I

a. The primary windings of the matching transformer form a star connection, the switching elements 20 and 21 being closed and the switching elements l6, l8 and 22 being opened.

b. The primary windings of the matching transformer form a delta connection, the switching elements 20 and 22 being closed and the switching elements 16, 18 and 21 being open. Such a circuit is shown in FIG. 10.

c. The primary windings of the transformer are connected in a star pattern and are connected to the supply mains through a current-limiting inductance 19, the

switching elements 21 being closed and the switching elements 16, 18 and 20 and 22 being open. Such a circuit is illustrated 'in FIG. 11.

d. The primary windings of the transformer form a delta connection and are connected to the supply mains through current limiting inductances 10, the switching elements 22 being closed and the switching elements 16, 18, 20 and 21 being open. FIG. 12 illustrates such a circuit.

The possibility of the primary windings of the matching transformer being connected in star and delta patterns widens the range within which the supply voltage may be varied with the supply source functioning as a voltage source.

As should now be apparent, the objects initially set forth at the outset of the specification have been successfully achieved. Accordingly,

What is claimed is:

1. A device which is connectible as a voltage source or a current source for supplying power to an electron beam heating apparatus load, said device comprising a matching transformer and reactive elements connect- I able therewith for forming one of a voltage source and a current source for supplying power to said load, and switching means for selectively switching said reactive elements in and out of circuit with said transformer for selectively changing the electrical characteristics of the supply to provide a current source wherein the value of current supplied is substantially independent of the resistance value of the load, and to provide a voltage source wherein the value of voltage supplied is substantially independent of the resistance value of the load.

2. A device as defined in claim 1, wherein said reactive elements comprise both inductors and capacitors. 3. A device as defined in claim 1, wherein a three phase line supply is utilized, and wherein said matching transformer includes a primary and a secondary winding and wherein said electron beam heating apparatus is coupled to said secondary winding, one terminal of said primary winding being coupled to one terminal of the three-phase line supply, theother terminal of said primary winding being respectively connected to second and third terminals of a three-phase line supply through first and second circuits respectively, said first circuit including a capacitor and a first switch connected in series therewith, said second circuit including an inductor and a second switch connected in shunt therewith, said device exhibiting the characteristics of a current-source when said first switch is closed and when said second switch is open, the device exhibiting the characteristics of a voltage source when said first switch is open and when said second switch is closed, said capacitor and inductor constituting the reactive elements and said first and second switches constituting the switching means.

* l II! 

1. A device which is connectible as a voltage source or a current source for supplying power to an electron beam heating apparatus load, said device comprising a matching transformer and reactive elements connectable therewith for forming one of a voltage source and a current source for supplying power to said load, and switching means for selectively switching said reactive elements in and out of circuit with said transformer for selectively changing the electrical characteristics of the supply to provide a current source wherein the value of current supplied is substantially independent of the resistance value of the load, and to provide a voltage source wherein the value of voltage supplied is substantially independent of the resistance value of the load.
 2. A device as defined in claim 1, wherein said reactive elements comprise both inductors and capacitors.
 3. A device as defined in claim 1, wherein a three phase line supply is utilized, and wherein said matching transformer includes a primary and a secondary winding and wherein said electron beam heating apparatus is coupled to said secondary winding, one terminal of said primary winding being coupled to one terminal of the three-phase line supply, the other terminal of said primary winding being respectively connected to second and third terminals of a three-phase line supply through first and second circuits respectively, said first circuit including a capacitor and a first switch connected in series therewith, said second circuit including an inductor and a second switch connected in shunt therewith, said device exhibiting the characteristics of a current-source when said first switch is closed and when said second switch is open, the device exhibiting the characteristics of a voltage source when said first switch is open and when said second switch is closed, said capacitor and inductor constituting the reactive elements and said first and second switches constituting the switching means. 